It is desirable that map data used in a navigation device accurately express the current conditions of roads, facilities and so on, which vary constantly. Hence, in a well-known system, new map data are distributed via a communication network, and the map data in a map database of a navigation device are updated using the distributed map data. In another well-known system, in order to manage the update condition of the map data on the navigation device side when updating the map data in this manner, identification symbols (map numbers) are allocated respectively to the plurality of map data stored in the map database, and update versions (version numbers) are allocated in accordance with the respective identification symbols of the map data (see Japanese Patent Application Publication H04-349575, for example).
In this type of system, when the update version of map data on a server device side is later than the update version of the corresponding map data on the navigation device side and the two sets of map data have been allocated with the same identification symbol, the latest map data is transmitted to the navigation device from the server device. Upon reception of the newest map data, the navigation device updates the map data in the map database by replacing the old map data with the latest map data. Also at this time, the navigation device performs management by modifying the update version of the map data to the latest update version.